A Spectral Shaper Based Two-Tap RF Self-Interference Canceller for Full-Duplex Radios

A simple and effective two-tap RF Self-Interference Cancellation (SIC) circuit is proposed for in-band Full-Duplex radio. Conventional techniques deal with phase-based RF cancellation which inherently results in non-flat spectrum (especially for wideband signals). Any conventional second cancellation stage cannot significantly improve SIC in the RF domain due to this non-flat Residual RF spectrum. This work proposes a novel “Spectral shaper” that improves SIC by 16dB on a 20MHz bandwidth RF signal, validated through experimental measurements on a discrete prototype. This model, in conjunction with a circulator, offers a total of 62dB RF SIC, and is implemented here using readily available off-the-shelf components.